Method and apparatus for control of superheat by gas mass flow



Sept. 27, 1938. c. E. LUCKE METHOD AND APPARATUS FOR CONTROL OF SUPERHEAT BY GAS MASS FLOW Filed Aug. V 50, 1954 3 Sheets-Sheet l v A 1. A y 0 4 a o v a I INVENTOR TTORNEY Sept. 27, 1938. c, E CKg 2,131,058

METHOD AND APPARATUS FOR CONTROL OF SUPERHEAT BY GAS MASS FLOW Filed Aug. 50, 1934 3 Sheets-Sheet 2 Fig? Fig I3 INVENTOR Char/es E. Lac/(e A ORNEY Sept. 27, 1938.

c. E. LUCKE 2,131,058 METHOD AND APPARATUS FOR CONTROL OF SUPERHEAT BY GAS MASS FLOW Filed Aug. 30, 1934 3 Sheets-Sheet 3 INVENTOR. Chaf/es E. Lucke ATTORNEY.

Patented Sept. 27, 1938.

UNITED ST TES PATENT OFFICE METHOD AND APP ARATUS. FOR- CONTROL OF SUPERHEAT BY GAS MASS FLOW Charles E. Lucke, New York, N. Y., assignor to The Babcock & Wilcox Company, Newark,

J., a corporation of New Jersey Application August 30, 1934, Serial No. 742,048

- 9 Claims.

This invention relates to fluid heat exchange apparatus in which heat is transferred from hot gases sweeping across spaced tubes, to a fluid within the tubes. The invention is herein ex- 6 emplified as an interdecl superheater.

An object of the invention is to maintain a consurface at a given total flow rate.

A specific object of the invention is to provide a superheater in which the gas mass flow over. part of the superheater surface is varied for the purpose of obtaining a more constant superhea't, in-

sweep the superheater heating surface.

Other objects of the invention will appear as the accompanying description proceeds.

eating different adjustments of the illustrative apparatus, all three of them for boiler load condiso tions which are intermediate those of light load.

and full load.

Fig. 4 is a diagrammatic view indicating the adjustment of the apparatus when the boiler is under full load.

35 Fig. 6 is a diagrammatic view of the apparatus indicated in Fig. 1 of the drawings, illustrating a 40 boiler load.

In Fig. 1 of the drawings there is shown an 55 water drum 34 is connected to the headers 30 and,

32 in a well known manner by horizontal circulators 36and do'wntake nipples 38.

It has been an undesirable characteristic of convection superheaters that they do not maintain a constant superheat when the boiler load 6 changes. They naturally operate so as to provented by this invention through the application 10 superheat as the boiler load increases. 1

Investigations of heat transfer have proven that the unit rate in B. t. u./hr./sq'. ft./degree between the hot gas and the tubes increases with an increase of gas mass flow, lb. of gas/hr./sq. ft.

' of mean stream section, and in a regular manner.

When the boiler load is lig t the'gas temperature increase of gas mass flow at light load. This is the superheater tubes so that at light load there is a lesser flow area or gas stream cross section and consequently a higher gasmass flow. This increases the unit heat transfer rate and increases Considering the apparatus as it is shown in Fig.

stance by the upright fixed bafiies and 42 and 40 Fig. 1 shows two movable baflles 44 and 46 which are preferably pivoted at 48 and 50 upon supports 52 and 54 secured tothe steam generas shown in dotted lines in Fig. 1 the furnace 2 in substance, operate as a solid baflie extendin along the upper tu es of the lower bank of steam generating tubes to prevent fiow of gases from the furnace directly upward.

There are threemore pairs of movable baffles. one pair above the gas pass between the fixed baflle 46 and the wall 26, and a pair at the top and bottom of the gas pass between the two fixed baiiles 46 and 42. Such-baffles are indicated by may have the in response to changes 15 sponse to changes in numerals 55-66 inclusive. These movable baii'ies positions indicated by the full lines in Fig. 1, or those indicated by the dotted lines, or any intermediate position. The full line positions are for light boiler load. The gases then make three passes in series over the superheater, while the dotted line' positions allow the gases to make a single pass in three parallel sections for full boiler load. The full load position provides about three times the gas flow area and one third the gas mass flow of the light load position, and intermediate positions permit of graduation of area and mass fiow between these limits.

Each of the movable baflles above described may be provided with any suitable mechanism for holding it in open or closed position or in any intermediate position so as control of the mass flow of gases acrossthe superheater. All of these movable bafilesare shown moved to their open positionfor full load inFig. 4 of the drawings. Y f

In Figs. 2, 3 and 5 the movable baffles are shown in intermediate positions for a boiler load betwen a full load or a light load.

It is an outstanding characteristic of the pres- .ent inventionthat all of the furnace gases must beyond the superheater surfaces, wherein there are two separate gas streams of such widely variant temperatures as exist in the case wherein some of the furnace gases are by-passed around the superheater.

Regulating apparatus to cause the mass flow of the gases across the superheater to be so varied in boiler load that excessiv'e changes in superheat are prevented, is indicateddiagrammatically in Fig. 6 of the drawings. Referring to this figure, and boiler load as changing from light to full load, the first loadincrease causes the diaphragm operator 62 to move the dampers 51 and 56 'to their open position. The next increase causes the dampers 55, 56, 56 and 66 to be simultaneously moved to their open positions by action of the operator 64. A further increase involves the action of the operator 66 in opening the dampers 44 and 46.

The diaphragm operators may be operated in sequence through changes in the fiuid pressure in the line 66, caused by a proper shaping of the lands 10 and 12 of a pilot valve 14 which may be of the nature of the valve shown in the patent to Johnson No. 2,054,464,, dated-Sept. 15, 1936, and the axial movement of the valve stems of the spring loaded operators 64 and 66 may be mechanically amplified, or hydraulically amplified by the use of such a mechanism as that indicated in the patent to Jones 1,972,853, September 11, 1934, or the patent to Albright 1,922,834,- August 15, 1933.

The pilot valve rod 16 may be operated in reboiler lead through such Furthermore, air is constantly to effect any desired so as to have a tendency Bourdon tube 60 may apparatus as that shown in Fig. 6. Here, this rod is connected to ,a lever 16 linked to a Bourdon tube 66 actuated by temperature changes in the fiuid in the capillary 62 which communicates with a member 64 sensitive to temperature changes in the superheater outlet header 12.

The lever 16 may also be subject to control by a fiow meter 66 which uses saturated steam pressure through the line 66 and superheater outlet pressure through flow of steam, or boiler load.

With further reference to the pilot valve 14 and its operation, the space between the two lands 16 and 12 is constantly under air pressure.

lands on all sides, in order to have an effect in the nature'of a lubricating eflect, upon the lands. This circumferential air stream is, however, so thin that the air pressure may be maintained in thespace between the lands. so shaped that the flow of air from the space between the lands 16 and 12 into the line 66 increases as the land 12 moves downward from a position wherein its position of maximum diameter is just above tube 66, the maximum pressure being created in the line 66 when the top of the land 12 has moved well below the axis of the inlet of the tube 66.

The Bourdon tube 66 is responsive to temperthe line 66 as a measure of the 10 flowing past the The land 12 is 20f the axis of the inlet of the g5 ature changes in the superheated steam in the header l2, and when that temperature increases the free end of the Bourdon tube will be elevated, to elevate the left hand end of the lever 16 through the link connecting the lever to the Bourdon tube. If this action 5 causes the pilot valve rod 16 to be raised, the land 12 will be raised and the pressure in the line 66 will be decreased. However the influence of the be counteractedby the infiuence of the fiow meter 66 which uses the differ-' 4o ence between saturated steam pressure in the line 66 and the pressure of the superheated steam in the line 66 as a measure of steam flow. Whensteam fiow increases, the action of the flow meter 66 tends to elevate the right hand end of the lever 16 and pivot it around its connection with the link depending from the Bourdon tube 66. If this fulcrum point remains fixed the pivot valve rod 16 will be lowered and the fluid pressure in the line 66 will be increased.

What is claimed is:

1. In combination, a steam boiler including a bank of steam generating tubes, a furnace from which hot gases pass across the steam generating tubes, a superheater contacted at all times.

by all of the gases which have passed across the generating tubes, a first set of gas flow regulators contacting with the furnace gases before they reach the superheater, gas baffling means beyond said set of regulators and defining gas flow passages across said s perheater, and another set of gas fiow regulators positioned beyond the superheater with reference to gas flow and cooperable with the first set of flow regulators and with said baflling means to cause the gases to pass across the superheater in a single pass or in a plurality of passes, said sets of regulators cooperating to cause the mass'fiow of the gases across the superheater ,tobe varied.

2. In combination, afurnace, steam generating tubes across which gases pass from the furnace, a superheater having tubes positioned beyond the steam generating tubes relative to gas fiow and arranged so that all of the furnace gases must at all times contact with superheater surface, a battle transversely related to the supersuperheater surface at low boiler load and a uniheater tubes, and gas flow controllers so assoformly low mass flow over the entire superheater heater surface in inverse ratio to changes in boilversely to boiler load changes. er load or superheater steam exit temperature '7. In a steam boiler, a furnace, a bank of steam and thereby prevent excessive variations of the generating tubes extending across the gas flow latter, there being a plurality of the controllers from the furnace, a superheater including spaced forwardly of the superheaterand beyond the sutubes positioned beyond the generating tubes with upon the boiler. forwardly and rearwardly of the superheater 3. In the production of superheated steam-for with reference to gas flow, said dampers 00- power purposes, causing the mass flow of heating acting with the baffles to cause the gases to face and superheating surface in series, causing CHARLES E. LUCKE. 

